(a) Field of the Invention
The present invention relates to an X-ray tube.
(b) Description of the Related Art
An X-ray tube uses principle the fact that when a high voltage is applied between a cathode and an anode, a thermal electron source generated in the cathode configured as a filament collides with the anode as a metal to collide with electrons of the metal, producing X rays.
The interior of the X-ray tube is maintained in a vacuum state to prevent molecular ionization in a movement path of high energy electron beams, thus preventing damage to the electron source due to dielectric breakdown or ion collision. A thickness of a target is determined in consideration of a transmission depth of electrons and absorption capability of heat generated by the target.
Here, in the X-ray tube, electrons emitted from the cathode are accelerated in the vacuum state to collide with the anode target, about 1% of electron energy is generated as X rays and about 99% of energy becomes heat energy according to bremsstrahlung, and thus an allowable thermal load of the anode target is directly related to an output of an X-ray source.
Meanwhile, an X-ray tube is divided into a fixed X-ray tube and a rotational X-ray tube according to a way in which an anode operates. A rotational X-ray tube is substantially the same as a fixed X-ray tube, except for a function of dispersing heat generated by a target according to rotation of an anode.
FIG. 1 is a view illustrating a rotational X-ray tube according to the related art. Referring to FIG. 1, the related art X-ray tube employs a thermal electron source and a magnetic electron lens, in which a vacuum container 2 having a thermal electron source at the left is positioned within a container 1 filled with cooling insulating oil, and supports a bearing 6 to allow a rotational shaft 3 to rotate.
A path of electron beams emitted from the thermal electron source is bent due to a magnetic lens 5 outside of the vacuum container 2 to reach a sloped anode 4 target, producing X rays. The related art X-ray tube is advantageous in that the rotary anode 4 may effectively release (or dissipate) heat through the cooling insulating oil.
However, X-rays cannot be switched at a desired time due to a limitation in the thermal electron source.